1. Field of the Invention
The present invention relates to an installation structure of a solar cell module array, an installation method for installing solar cell modules, a wiring method for wiring string cables of solar cell module strings, and a sunlight power generation system. The term "solar cell module" in the present invention typically indicates a module which comprises a photovoltaic element group sealed by way of resin-sealing, said photovoltaic element group comprising a plurality of photovoltaic elements electrically connected with each other. The term "solar cell module string" indicates an integral circuit comprising a plurality of solar cell modules electrically connected with each other in series connection. The term "solar cell module array" indicates an array in which a plurality of solar cell module strings are arranged while being electrically connected with each other in parallel connection.
2. Related Background Art
In recent years, societal consciousness of environmental and energy problems has been increasing all over the world. Particularly, heating of the earth because of the so-called greenhouse effect due to an increase of atmospheric CO.sub.2 has been predicted to cause a serious problem. In view of this, there is an increased societal demand for early realization of a power generation system capable of providing clean energy without causing CO.sub.2 buildup as in the case of thermal power generation.
As such a power generation system, public attention has been focused on a sunlight power generation system (that is, a solar cell power generation system) for the reason that it is a clean power generation system which generates electric power using sunlight, which is evenly accessible at any place in the world, as the power generation energy source, and which can attain relatively high power generation efficiency without requiring a complicated large installation, and can be expected to comply with an increase in the demand of electric power in the future without causing environmental destruction. It is expected that the use of such a sunlight power generation system will widely spread not only at private residential buildings, but also at public facilities in the near future. It is also expected that the sunlight power generation system would be used at power generation facilities in the future.
Presently, sunlight power generation systems have been used at certain private residential buildings and also at certain public facilities. It is expected that the number of private residential buildings and public facilities where a sunlight power generation system is used will gradually increase in the near future.
As such a sunlight power generation system, there have been proposed, for instance, a trestle installation type solar cell module comprising a framed solar cell module installed on a trestle provided on a roof, a building material integral type solar cell module comprising a solar cell module integrated with a building material, and a roofing material integral type solar cell module comprising a solar cell module integrated with a roofing material. Various studies have been conducted in order to improve these solar cell modules. Particularly, said building material integral type solar cell module and roofing material integral type solar cell module excel in execution work efficiency and exterior appearance and because of this, extensive studies have been conducted in order to further develop these solar cell modules.
FIGS. 2(a) and 2(b) show the constitution of an example of a typical conventional solar cell module (or a solar cell panel). In FIGS. 2(a) and 2(b), reference numeral 201 indicates a surface side covering member, reference numeral 202 an inside filler, reference numeral 203 a photovoltaic element, reference numeral 204 a back side covering member, and reference numeral 205 a frame. Reference numeral 206 indicates a terminal box for outputting a power which is provided at a rear face of the back protective member 204. Reference numeral 207 indicates a connection cable which is extended from the terminal box 206. The front side protective member 201 comprises a tempered glass plate having a thickness of about 3 mm. The back side covering member 204 comprises a resin film having weatherability such as a TEDLAR [trademark name, comprising PVF (polyvinyl fluoride)] film. The inside filler 202 is interposed between the front side protective member 201 and the back side covering member 204, where the photovoltaic element 203 is sealed by the inside filler 202. As the inside filler 202, EVA resin (ethylene-vinyl acetate copolymer) excelling in weatherability is used in many cases.
In the case where such a solar cell module is installed on a roof of a building, such problems as will be described below are liable to occur.
Japanese Unexamined Patent Publication No. 86066/1996 discloses that when a fire occurs near the building, the fire spreads to the building, and the solar cell module situated on the roof thereof is exposed to a flame or heat radiated from the spreading fire; there is a fear that the glass plate of the solar cell module will break due to the flame or heat, where the EVA as the inside filler is heat-fused or burned to flow to the outside.
Besides, Japanese Unexamined Patent Publication No. 148614/1997 discloses that when a fire occurs near the building and the fire spreads to the building, there is a fear that the glass plate as the front side protective member of the solar cell module will break due to heat radiated from or flames from the spreading fire, where the broken glass plate is scattered or the EVA as the inside filler is heat-fused to flow to the outside to cause firing at the underlayment of the roof.
Thus, for such a solar cell module having the configuration shown in FIGS. 2(a) and 2(b), it is understood that there are problems such that when a fire occurs near the building whose roof having the solar cell module installed thereon, the glass plate as the surface side protective member of the solar cell module is heated by the flame of or the heat radiated from the spreading fire to break and the EVA as the inside filler is heat-fused or burned to flow to the outside.
Separately, in the case where the solar cell module is used as a power generation source by installing it on the roof of a building, it takes such a manner as will be described in the following. That is, there are provided a number of given solar cell modules, a predetermined number of these solar cell modules are electrically connected with each other in series connection to obtain a plurality of solar cell module strings, and these solar cell module strings are electrically connected with each other by means of string cables to establish a solar cell array on the roof.
As a result of experimental studies by the present inventors of this solar cell array, there was obtained a finding that there is an occasion such that when a fire occurs in the vicinity of the solar cell array, the coating of some of the string cables is broken by heat radiated from the fire to cause leakage or the coatings of the string cables are melted by said heat, whereby the cables are mutally electrically contacted and, as a result, they are shorted.
In the past, substantially no consideration has been made of this situation which will occur at the string cables provided at the time when the solar cell modules are installed on the roof of the building.
Thus, in the prior art, such cases as will be described below are found upon wiring the string cables into the building.
(1) A case wherein regardless of the positive and negative polarities, the string cables are gathered and they are drawn into the building through an entrapment hole provided at the roof. PA1 (2) A case wherein until the string cables are drawn into the building, the string cables of positive polarity and those of negative polarity are crossed and contacted with each other.
In the case where the wiring of the string cables is performed as described in the above case (1) or (2), when some of them have an exposed portion, there is an occasion for these string cables to contact each other. In this case, there is a fear that electrical short will occur among them.
When the string cables having such an exposed portion contact each other, since they are electrically connected to an inverter provided with a DC circuit earth-fault detector having a function of detecting the occurrence of such an electrical short to a certain extent, it is considered that occurrence of a secondary calamity or the like could be prevented beforehand.
However, there is an increased demand for not only further improving the safety but also providing a more secure safety measure.